The Contractor known as Hei returns to Tokyo with his companion Yin to investigate a new threat: a flower called the Black Dandelion that grants Contractor-like powers to anyone who touches it. Police officer Misaki Kirihara reopens her hunt for the elusive BK201 as the trail behind the flower leads to a man called Harvest, pulling Hei back into the shadows he'd tried to leave behind. This manga continues the story from the original Darker than Black anime.